From 9d13c3d892ba67696b3193eb20eef51ef498470a Mon Sep 17 00:00:00 2001
From: Mike Cifelli <michael.cifelli@gmail.com>
Date: Wed, 14 Mar 2018 21:01:39 -0400
Subject: [PATCH] Disallow appending improper lists

---
 src/function/builtin/cons/APPEND.java      |  9 +++++++++
 test/function/builtin/cons/APPENDTest.java | 11 +++++++++++
 2 files changed, 20 insertions(+)

diff --git a/src/function/builtin/cons/APPEND.java b/src/function/builtin/cons/APPEND.java
index 2e95e02..fd4c5a1 100644
--- a/src/function/builtin/cons/APPEND.java
+++ b/src/function/builtin/cons/APPEND.java
@@ -46,8 +46,10 @@ public class APPEND extends LispFunction {
     }
 
     private ArgumentValidator argumentValidator;
+    private String name;
 
     public APPEND(String name) {
+        this.name = name;
         this.argumentValidator = new ArgumentValidator(name);
         this.argumentValidator.setExactNumberOfArguments(2);
         this.argumentValidator.setEveryArgumentExpectedType(Cons.class);
@@ -60,8 +62,15 @@ public class APPEND extends LispFunction {
         Cons rest = (Cons) argumentList.getRest();
         Cons firstList = (Cons) argumentList.getFirst();
         Cons secondList = (Cons) rest.getFirst();
+        validateLists(firstList, secondList);
 
         return append(firstList, secondList);
     }
 
+    private void validateLists(Cons firstList, Cons secondList) {
+        ArgumentValidator properListValidatorOne = new ArgumentValidator(name + "|list-one|");
+        ArgumentValidator properListValidatorTwo = new ArgumentValidator(name + "|list-two|");
+        properListValidatorOne.validate(firstList);
+        properListValidatorTwo.validate(secondList);
+    }
 }
diff --git a/test/function/builtin/cons/APPENDTest.java b/test/function/builtin/cons/APPENDTest.java
index e6b3e1a..38ce2b2 100644
--- a/test/function/builtin/cons/APPENDTest.java
+++ b/test/function/builtin/cons/APPENDTest.java
@@ -7,6 +7,7 @@ import static testutil.TestUtilities.parseString;
 import org.junit.Test;
 
 import function.ArgumentValidator.BadArgumentTypeException;
+import function.ArgumentValidator.DottedArgumentListException;
 import function.ArgumentValidator.TooFewArgumentsException;
 import function.ArgumentValidator.TooManyArgumentsException;
 import testutil.SymbolAndFunctionCleaner;
@@ -51,6 +52,16 @@ public class APPENDTest extends SymbolAndFunctionCleaner {
         assertSExpressionsMatch(parseString("(4 5 6)"), evaluateString("y"));
     }
 
+    @Test(expected = DottedArgumentListException.class)
+    public void appendWithDottedFirstList() {
+        evaluateString("(append '(1 2) (cons 3 4))");
+    }
+
+    @Test(expected = DottedArgumentListException.class)
+    public void appendWithDottedSecondList() {
+        evaluateString("(append (cons 1 2) '(3 4))");
+    }
+
     @Test(expected = TooManyArgumentsException.class)
     public void appendWithTooManyArguments() {
         evaluateString("(append () () ())");